Molded rubber products often contain fabric reinforcement. The fabric is typically prepared by coating the cord, or fabric, by passing it through an aqueous latex followed by drying the coated cord. In such a cord dipping procedure, the dried polymer coating obtained on the cord provides an adhesive base for adhering rubber to the fabric. The rubber is generally applied to the cord with the aid of heat and pressure such as by calendering.
The cord to rubber adhesion is complex in nature and dependent largely upon the ability of the coating on the fabric to remain resistant to oxidative degradation, such as while the fabric is being stored prior to use, during application of rubber to the coated fabric and during utilization of the reinforced rubber. Degradation of the coating such times can result in an inferior adhesion to rubber and could well result in a delamination of the rubber from the fabric in the finished article, particularly during use.
Certainly degradation of various elastomers due to environmental conditions is well known. Rubbery coatings when deposited from copolymer latices and used as fabric adhesives have been known to lose their elasticity and to even split or crack when subjected to oxygen at elevated temperatures. It is generally recognized that oxygen and ozone, as well as ultraviolet light, are major causes of such degradation and generally considered detrimental to rubber stocks themselves.
Resorcinol formaldehyde/vinyl pyridine latex blends (often called RFL's) are often used as tire cord adhesives as being applied to tire cords to enhance their adhesion to rubber. However, it is understood that adhesion of the treated cord to the rubber can be degraded or substantially reduced if the RFL coating is excessively exposed to environmental conditions prior to use.
It should be pointed out that it is often a general practice to simply dry cords which have been treated with latex adhesive, such as RFL, in a gas fired hot air oven during which the treated fabric can be subjected to the combustion products of the oil. With such procedures, it has sometimes been observed that the adhesive has been sufficiently degraded that an early failure of a cord/rubber composite occurred involving a delimination of the rubber from the cord. Although this delamination may have primarily been due to the determination has not been fully verifed.
The use of an antioxidant would be expected to improve the resistance of the polymeric coating on the cord to oxidative degradation. However, there is apparently a hesitation to use antioxidants in the fabric aqueous latex dip for various reasons. For example, an antioxidant can conventionally be added to a latex in an emulsion form. However, the presence of additional foreign materials, such as emulsifiers, can become a residue on the coated cord and can adversely affect its adhesion to rubber. In addition, the cord-dip process typically requires the use of relatively dilute or diluted latex of relatively low solids content. Dilution of a latex containing an antioxidant could reasonably be expected to cause a precipitation or setting out of the antioxidant from the latex. Indeed, a low solids content of a diluted latex can particularly be susceptible to precoagulation.
Thus, it is desirable that a method be derived, or provided, for providing a reasonably stable aqueous cord dip and coated cords resulting therefrom having a resistance to atmospheric degradation.
Therefore, an object of this invention is to provide a coated cord or textile fabric thereof resulting from a latex having a degree of protection against oxidative degradation and rubber reinforced therewith. It is a further object to provide an aqueous latex dip, or coating, for textile cord having a degree of stability against pre-coagulation.